1. Field of the Invention
The present invention relates to a method of producing a semiconductor base member having a nonporous layer formed on a porous layer and a method of using this semiconductor base member to produce a semiconductor member such as an SOI wafer.
2. Related Background Art
In order to manufacture a light emitting element or an SOI wafer, it is necessary to prepare a semiconductor base member having a porous layer and a nonporous layer formed thereon.
An example of preparation of the semiconductor base member will be described with reference to FIGS. 9A to 9F.
As shown in FIG. 9A, a silicon base material 1 such as a CZ silicon wafer having a polished surface is prepared and at least its surface is made porous by anodization or the like.
After the inner wall surfaces of pores in a porous layer 2 are oxidized, the silicon base material is cleaned with a dilute hydrofluoric acid to remove an oxide film from the surface of the porous layer 2.
As shown in FIG. 9B, the porous layer 2 is subjected to a heat treatment in a hydrogen-containing atmosphere, and a silicon-containing gas is then introduced to epitaxially grow a nonporous layer 3.
As shown in FIG. 9C, the surface of the nonporous layer 3 is oxidized to form an insulating film 4.
As shown in FIG. 9D, a first member comprising a silicon base material 1 having the porous layer 2, the nonporous layer 3, and the insulating layer 4 is bonded to a second member 5 separately prepared to form a multilayer structure having the nonporous layer 3 inside.
As shown in FIG. 9E, the silicon base material 1 is removed. The method for removing the silicon base material 1 includes a method of eliminating the silicon base material 1 itself by grinding, polishing, or etching from the back surface and a method of cracking the inside of the porous layer 2 and/or its interface to separate and remove the silicon base material 1.
As shown in FIG. 9F, the porous layer 2 remaining on the surface of the second member 5 is removed to obtain an SOI wafer having the nonporous layer 3 formed on the second member 5 via the insulating layer 4.
The above method is disclosed in Japanese Patent Application Laid-Open No. 5-21338 (Japanese Patent No. 2608351), U.S. Pat. No. 5,371,037, U.S. Pat. No. 5,856,229, Japanese Patent Application Laid-Open No. 9-102594, and Appl. Phys. Lett. 64, 1994, p. 2108, and the like.
However, there is a demand for further improvement of the quality of the nonporous layer formed on the porous layer, in particular, surface smoothness and crystal defects.
For example, in the above method for producing an SOI wafer, when the surfaces to be bonded are not smooth, a void, that is, a non-bonded area which is observed by ultrasonic waves or infrared transmitted light is easily generated in bonding.
In addition, in producing a device such as an MOS transistor using the nonporous layer, metal impurities may be conventionally segregated into crystal-defect sites. When metal impurities are segregated into crystal-defect sites, the device characteristics is easily degraded.